Seaworthy Magazine: Thunderstorms - A Few Members' Accounts
Living and sailing in the mid-west has given us the opportunity to experience thunderstorms on many occasions. Three thunderstorm episodes while sailing came to mind when Seaworthy requested reader experiences. In each instance the storms came up at night while we were anchored.
First, some thunderstorm background, there are four attributes to a thunderstorm: 1. Precipitation - Rain and or hail. The record for Minneapolis is 12 inches of rain from a thunderstorm in less than three hours. In most cases rain or hail is an inconvenience, however, one should consider what would happen to your snug harbor if there were a flash flood, because of massive rainfall upriver. 2. High winds - Thunderstorms are usually accompanied by "micro-bursts". Short duration (less than an hour) periods of intense wind. Fifty to sixty knot winds are not uncommon. 3. Lightning - Without a doubt lightning is the most dangerous aspect of a thunderstorm. More people die annually in the U.S. from lightning strikes than any other weather phenomena. 4. Thunder - While this may be the most frightening aspect of a thunderstorm, in truth it may be the most helpful. From an early age in thunderstorm country you learn to "time the thunder." Since lightning is the real killer, thunder can help you tell how close a lightning flash is to you. This is based on the concept that light travels at 186,000 miles per second and sound travels at a little over 1,000 feet in a second, or about five seconds to cover a mile. When you see a particularly vivid flash you begin counting one thousand one, one thousand two, etc. If you get to five before you hear the thunder, the lightning strike is about a mile away. When the flash and bang are almost simultaneous, you are talking hundreds of feet or less. I don't know if "timing the thunder" is of much real use but it can be a comforting distraction in a very tense situation.
As novice charters in 1988, my wife, Peggy, and I, together with our two teenage children, rode out our first thunderstorm in a 27' Hunter anchored in Raspberry Bay in the Apostle Islands of Lake Superior. You could see the storm off in the distance as night fell. We had all settled in when it hit. Winds went from a breeze to a gale in minutes. The boat heeled back and forth wildly and lightning cashed all around us. Everyone stayed below and away from the mast, as several flash-bang strikes needed no timing. I did not go on deck to check the wind velocity; sometimes fear can overcome curiosity, but we were told that there had been gusts over 50 knots. In an hour it was all over. The one thing that Peggy and I came away with from this experience was that it was really nice to have our anchor well set and with plenty of scope. We are firm believers in seven to one scope as a minimum and, when in doubt, 10 to one is better.
A few years latter we anchored out in Julian Bay in the Apostles. This time there was warning via weather service radio of thunderstorms. We reset the anchor in a more protected location away from other boats with ten to one scope. The lightning crashed, the wind blew 50 knots and clocked through 360 degrees but we stayed put. I did go on deck during this episode to make sure that we were not twisting out the anchor and dragging with the wind shifts.
Our third experience was the evening of July 4th.this last summer in Big Bay off Madeline Island in the Apostles. This storm was the remnant of a storm that flattened thousands of acres of trees in northern Minnesota. We were forewarned, so we made our usual anchoring preparations. Unfortunately, Big Bay does not offer the kind of protection that one should have in these kind of conditions. We were treated to an awesome display of lightning including cloud to cloud directly over head. Then came fierce 60-knot winds, with buckets of rain and hail. Due to our less protected position, I went on deck to start the motor. (A good set of foul weather gear is really nice!) If need be, I could take some strain off the ground tackle, react if we did drag, but also I wanted to keep an eye on other boats anchored near us. Unfortunately our motor would not start (another story). We were not on a lee shore and the ground tackle held and the other boats stayed put. I have become aware that others are not so obsessed with setting and often resetting their anchors as we are. We also get some astonished looks when we mention 10 to one scope.
Keep your eye and ear peeled in thunderstorm country. Whether, out on open water or at anchor, get set for a big blow. When the rain, wind and lightning come is not the time to get the anchor better set or sails reefed or put away. I know I don't know enough about preventing damage or injury if struck by lightning. Lightning is really the most frightening part of these storms for me.
Hurricanes and tornadoes are the destructive superstars of the weather world, but thunderstorms can pack quite a punch and you are probably 100 times more likely to have to deal with one.